Dormancy in Brine Shrimp Embryos

by Tony A. Fitz

The scientific literature recently provided information that may be useful for aquarists who hatch brine shrimp (artemia). Science magazine of 18 March 1988 contains an article concerning dormancy in artemia embryos. During times of unfavorable environmental conditions, artemia embryos can go into a state similar to suspended animation. This dormancy occurs while the embryo is in brine and should be distinguished from the well-known and convenient dormancy which occurs when the cysts are dry. The suspended animation during the wet state is related to changes in the levels of acidity inside the embryo, in which the intracellular pH decreases markedly (the amount of acidity goes up). The state of suspended animation helps the embryo survive until the world outside is not quite so cruel.

Why is this of interest to the aquarist? It means that brine shrimp cysts are unlikely to hatch during unfavorable conditions, which is not surprising. Of greater interest is that the cysts can survive during bad times, hopefully to hatch when conditions improve. Of importance, this implies strongly that acidic water will decrease the hatching rate.

The tap water in my neighborhood tends to be slightly acidic and various metabolic events in water tend to increase the content of acidity. I have heard complaints from other area aquarists of strongly acidic aquarium water. Acidic water should not be used to hatch brine shrimp, since this instead will promote dormancy in the artemia embryos.

Pure "salt" (sodium chloride) has no buffering capacity. Pure salt therefore has no effect on water pH; if the water is acidic to start with, it will remain acidic after the addition of any amount of sodium chloride. To ensure alkaline water conditions for our artemia hatching vessels, we should not use pure salt unless we also add an appropriate buffer to keep the water at a slightly alkaline pH. Several adequate buffers are available commercially to buffer water into the slightly alkaline region. I believe that the easiest, and therefore the best, way to achieve slightly alkaline pH is to use plain old cheapo rock salt in artemia hatching containers.

Common, ordinary, generic rock salt is great for several aquatic purposes. I refer to the stuff that is sold in any grocery store for melting ice off sidewalks and other "nonconsumable" purposes. Yes, I refer to that nasty looking stuff with black somethings in it that never completely dissolve in water. The cheaper it is and the junkier it looks, the more I like it.

I don’t know exactly what is in cheap rock salt, but after using many different brands from many different sources for many years (e.g., buying whatever was cheapest on the shelf of whatever store I was in at the time), I have never had any problems with rock salt and am convinced that its impurities are not harmful. The junk in rock salt may even be valuable for our aquatic uses. Not only are we undoubtedly getting trace minerals (maybe megatraces), but the rock salts that I have tested contain "secret ingredients" that conveniently tend to buffer water into the slightly alkaline region (interesting, isn’t it, that this is just what we want for hatching brine shrimp). I use rock salt not only for hatching brine shrimp, but I also put one teaspoon per gallon into all of my fry tanks (use caution for certain mineral-intolerant species such as Corydoras). This amount of salt in fry tanks keeps most newly hatched brine shrimp alive for at least 24 hours, so that one feeding daily ensures continuous availability of this most nutritious of fry foods. Whatever are the black stuffs and other secret ingredients in cheap rock salt, they obviously aren’t too bad since fragile fry thrive in it. I also add rock salt to all water containing Nothobranchius species, which otherwise quickly become extinct in my tanks.

Of course, it must be possible to get a bad batch of rock salt. To be prudent, one might use care with a new bag until its adequacy is demonstrated. Thereafter, an investment of a very few dollars in several bags of the same brand would secure a huge supply. And you can also use it to make ice cream in the summer and melt ice in the winter! Viva la cheapo rock salt.